Trial instrument assembly for use in a surgical procedure

ABSTRACT

A trial instrument assembly for use in a surgical procedure to replace an orthopaedic joint includes a trial implant having a stem portion for fitting within a prepared cavity in the patient&#39;s bone. The stem portion defines a stem axis. A neck portion is connected to the stem portion to protrude from the cavity when the stem portion is within the cavity. The assembly includes a plane guide that extends from the neck portion in a plane that is selected from (i) a plane perpendicular to the stem axis, and (ii) a plane parallel to the stem axis, for use in determining the location of the trial implant relative to an anatomical feature in a direction measured along the stem axis or perpendicular to the stem axis, respectively.

BACKGROUND TO THE INVENTION

This invention relates to a trial instrument assembly for use in asurgical procedure to replace an orthopaedic joint and to a method ofpreparing a bone to receive an implant component in such a surgicalprocedure.

The success of an operation to replace an orthopaedic joint with a jointprosthesis depends on factors that include: (i) selection of appropriatejoint prosthesis components; and (ii) accurate preparation of the boneso that the selected prosthesis components are properly located relativeto one another and to features of the patient's bone structure. Thesefactors can affect the fit of the prosthesis components in the patient'sbone. These factors can also affect the articulation of the jointprosthesis after implantation, in particular as to whether thearticulation of the implanted joint prosthesis accurately reproducesthat of the patient's healthy natural joint or some other sought jointconstruction.

A surgeon can make use of images of the patient's bones in apre-operative planning stage to identify appropriate prosthesiscomponents that will be appropriate to match a patient's anatomy. Theplanning stage can also include identifying details of steps in thepreparation of the patient's bone to receive the selected prosthesiscomponents.

It is normal to check the fit of a selected prosthesis component in acavity in a prepared bone. This can be done using a trial component thathas a shape similar to that of the ultimate implant component which isto be implanted.

SUMMARY OF THE INVENTION

The present invention provides a trial implant that provides a pluralityof tongues or grooves that can be engaged by a plane guide which, whenso engaged, extends beyond the trial implant allowing the position ofthe trial implant relative to an adjacent anatomical feature to beassessed.

Accordingly, the invention provides a trial instrument assembly for usein a surgical procedure to replace an orthopaedic joint, the assemblycomprising:

-   -   a. a trial implant having a body portion for fitting within a        prepared cavity in the patient's bone and a guide portion that        is connected to the body portion to protrude from the cavity        when the body portion is within the cavity, the guide portion        providing at least one first part of a projection and recess        assembly, and    -   b. a plane guide having a first portion that provides the second        part of the projection and recess assembly and engages the first        part of the assembly provided by the guide portion of the trial        implant to connect the plane guide with the trial implant, and a        second portion that, when the second part of the projection and        recess assembly provided by the first portion of the plane        guide, is engaged with the first part of the assembly provided        by the guide portion of the trial implant, and extends beyond        the end of the second part of the assembly where it engages the        first part of the assembly.

The invention also provides a trial instrument assembly for use in asurgical procedure to replace an orthopaedic joint, the assemblycomprising:

-   -   a. a trial implant having a stem portion for fitting within a        prepared cavity in the patient's bone, the stem portion defining        a stem axis, and a neck portion which is connected to the stem        portion to protrude from the cavity when the stem portion is        within the cavity, and    -   b. a plane guide which extends from the neck portion in a plane        that is selected from (i) perpendicular to the stem axis,        and (ii) parallel to the stem axis, to determine the location of        the trial implant relative to an anatomical feature in a        direction that is measured along the stem axis or perpendicular        to the stem axis, respectively.

The plane guide can be fixed to the trial implant. When the plane guideis fixed to the trial implant, the trial implant can be provided as oneof a set that differ from one another in one or more dimensions so thatthey correspond to different sizes of implant component. The plane guidecan be fixed to a guide portion of the trial implant that can beseparated from the stem portion thereof.

Alternatively, the plane guide can be fastened to the trial implant insuch a way that it can be separated from the trial implant. The planeguide can be fastened to the trial implant such that it can be movedrelative to the trial implant along an axis parallel to the stem axis(especially when the plane guide extends from the neck portion in adirection that is perpendicular to the stem axis), or along an axisperpendicular to the stem axis (especially when the plane guide extendsfrom the neck portion in a direction parallel to the stem axis).

The invention also provides a method of preparing a bone to receive animplant component in a surgical procedure to replace an orthopaedicjoint, the method making use of the assembly of the invention andcomprising:

-   -   a. positioning the body portion of the trial implant in a        prepared cavity in the patient's bone,    -   b. engaging the parts of the projection and recess assembly        provided by the first portion of the plane guide and the guide        portion of the trial implant, so that the second portion of the        plane guide extends beyond the trial implant,    -   c. assessing the position of the second portion of the plane        guide relative to an adjacent anatomical feature.

The invention enables the surgeon to assess the location of the trialimplant relative adjacent anatomical features. This information can beused by the surgeon to ensure that appropriate implant components areselected to suit the patient's anatomy, for example in terms of length,width, offset, version angle, and other variables that are available toa surgeon when selecting components to suit a particular patient'sanatomy. The information can also be used by the surgeon to determinewhether a cavity in a patient's bone has been prepared appropriately toensure that a selected prosthesis component is appropriately located inthe bone relative to other anatomical features.

The body and guide portions of the trial implant can be provided asseparate components that have formations by which the components can beconnected to one another. For example, the formations can comprise atleast one spigot provided on one of the components and a socket on theother of the components in which the spigot can be received. It can bepreferred to provide two spigots and two corresponding sockets, with onespigot-and-socket pair spaced apart from the other spigot-and-socketpair. It can be preferred that each of the body and guide portions has aspigot from one spigot-and-socket pair and a socket from anotherspigot-and-socket pair.

The provision of a trial implant in which the body and guide portionsare provided as separate components has the advantage that it allows thebody portion to be fitted into a prepared cavity in the bone without theguide portion in place. This can facilitate manipulation of the bodyportion, for example using manipulator instruments as is known.

The provision of a trial implant in which the body and guide portionsare provided as separate components also helps to reduce inventory,allowing different sizes of guide portions to be used with any bodyportion.

The assembly can include a trial neck component that can be fitted tothe body portion of the trial implant in place of the guide portion ofthe trial implant. The method of the invention can then include the stepof removing the guide portion of the trial implant from the body portionthereof, and fitting a trial neck component to the body portion of thetrial implant in place of the guide portion thereof.

The recess and projection assembly facilitates the alignment of thetrial implant and the plane guide where, when the projection is receivedin the recess, the body and guide portions of the trial implant arealigned, allowing the plane guide to be used to assess the position ofthe trial implant relative to an adjacent anatomical feature. Inparticular, the plane of the plane guide is fixed relative to the bodypart of the trial implant. The projection can be elongate so that itfits into a recess which is also elongate in the manner of a groove. Inparticular, the recess and projection assembly can be provided as atongue and groove assembly. The projection might have a differentconfiguration. For example, the projection could be provided as one ormore pegs. Such pegs might fit into respective sockets. Such pegs mightfit into one or more grooves. The use of one or more elongate recessesin the form of one or more grooves has the advantages of enabling theplane guide to slide relative to the trial implant without having todisconnect the plane guide from the trial implant completely, byallowing the projection (for example a tongue or one or more pegs) toslide within a groove in which it is received.

The guide portion of the trial implant can provide a plurality of firstparts of a projection and recess assembly. When the guide portionprovides more than one first part, it will frequently be preferred thatall of them are projection parts or that all of them are recess parts.

The shape of the opposite walls of the recess (for example groove) willbe selected so that the projection (for example tongue) is a snug fit inthe recess. It will frequently be preferred that the opposite walls ofthe recess are approximately parallel, at least over most of the depthof the recess, to accommodate a projection which has a constantthickness. The recess can be shaped so as to retain a projection in therecess, for example by being tapered slightly especially at its inwardedge which the projection is inserted towards.

Preferably a groove is open at least one of its ends. This can allow theprojection (for example a tongue) to be slid freely relative to that endof the groove. This can facilitate positioning of the plane guiderelative to the trial implant and to a feature of the patient's anatomy.

The projection should be a snug fit in the recess so that the secondportion of the plane guide is substantially fixed relative to the firstportion of the plane guide against movement out of the plane which isdefined by the projection and recess assembly. It can be preferred thatthe parts of the projection and recess assembly that are provided on thetrial implant are grooves and that the first portion of the plane guidedefines a projection that is a snug fit in a selected one of therecesses. At least the first portion of the plane guide can be a platethat is a snug fit in the or each groove on the guide portion of thetrial implant, the plate extending beyond the end of the groove.

The plane guide should be sufficiently rigid to ensure that it does notbend significantly especially in the second portion thereof where itextends beyond the end of the trial implant. This can be achieved by useof a plane guide which consists of a plate of a metal such as astainless steel, especially having a thickness of at least about 0.5 mm.

The plane guide can be provided by a sheet of material whose thicknessis selected so that the sheet is a snug fit in a groove on the guideportion of the trial implant. Accordingly, the thickness of the tonguethat is provided by the body portion of the plane guide is the same asthe thickness of the remainder of the sheet by which the plane guide isprovided.

The body and guide portions of the trial implant can be made from thesame material or from different materials. Materials that can be used tomake the body and guide portions of the trial implant can include metalsand polymeric materials. Examples of metals used in the manufacture ofsurgical instruments include certain stainless steels. Examples ofpolymeric materials used in the manufacture of surgical instrumentsinclude polyolefins, polycarbonates, PEEKs, polyamides, polyesters.Polymeric materials can be reinforced with fibrous material, especiallycarbon fibers. It can be preferred for the body portion of the trialimplant to be made from a metal that can withstand the forces to whichit is subjected when it is fitted in a prepared cavity in a bone. Theguide portion of the trial implant can be made from a polymericmaterial. This has the advantage of ease of manufacture, for example byuse of a molding technique.

The guide portion of the trial implant can provide two spaced-apartfirst parts of a projection and recess assembly that define first andsecond planes, the first plane being parallel to the second plane. Thetwo planes can correspond to different sizes of a component of animplant assembly ultimately implanted in the patient. Alternatively, thetwo planes can correspond to different positions of a component of animplant assembly within a patient's bone.

The guide portion of the trial implant can provide two first parts of aprojection and recess assembly which define first and second planes, thefirst plane being perpendicular to the second plane. The two planes candefine respective planes for the plane guide to locate it relative totwo different anatomical features.

The guide portion of the trial implant can provide combinations of one,two or more spaced-apart parts of a projection and recess assembly thatdefine first planes that are parallel to one another and one, two ormore spaced apart parts of a projection and recess assembly which definesecond planes that are perpendicular to the first planes.

The assembly of the invention can be used in procedures to replace partsof a joint or an entire joint. It can be used in procedures to replaceall or parts of hip, shoulder, knee, ankle joints. For example, the bodyportion of the trial implant can be a stem trial for use in preparingthe femur in a hip joint replacement procedure or for use in preparingthe humerus in a shoulder joint replacement procedure.

The invention is particularly suitable for use in preparing a cavity ina femur to receive the femoral stem component of a hip joint. The bodyportion of the trial implant can be a stem trial that is configured tofit in a prepared cavity in the patient's bone to replicate the fit ofan implant component in the cavity. The body portion of the trialimplant can be used to prepare the cavity in the bone to receive theimplant component in a subsequent step. For example, the body portioncan have one or more cutting teeth on its external surface by which thecavity is shaped to receive the implant component. The body portioncould also be used to compact the material on the surface of the cavityin a tamping step.

The guide portion of the trial implant can be mounted on the bodyportion. It can provide at least one projection or recess, preferably apair of parallel projections or recesses, (for example tongues orgrooves, especially grooves), arranged so that they extend in a planethat is approximately perpendicular to the superior-inferior axis,allowing the body portion of the trial implant to be located relative tothe greater trochanter. The guide portion of the trial implant can haveat least one projection and recess (for example tongue or groove,preferably at least one groove) that extends in a plane that isapproximately perpendicular to the medial-lateral axis, allowing thebody portion of the trial implant to be located relative to the lessertrochanter. The guide portion of the trial implant can be replaced by aneck trial. This can be appropriate once the step of locating the bodyportion of the trial implant has been completed. A trial head can bemounted on the trial neck for articulation relative to an acetabularbearing surface, provided by an implant component or trial or by thepatient's natural tissue.

INTRODUCTION TO THE DRAWINGS

Embodiments of the invention are described below by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a side view of a proximal femur with a trial implant whichcomprises a stem located within the intramedullary cavity with a guideportion fitted to it.

FIG. 2 is a side view of the guide portion of the trial implant.

FIG. 3 is a sectional elevation through the guide portion.

FIG. 4 is an isometric view of the guide portion.

FIG. 5 is a side view of the proximal femur with a trial implant thatcomprises a stem located within the intramedullary cavity with a trialneck and a trial head fitted to it.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 1 shows the proximal portion of a femur2 with a trial implant 4 located in a cavity within the femur. The femurhas been prepared by steps used conventionally in hip replacementsurgery. The assembly of the invention can be used in a surgical methodof implanting a femoral component of a hip joint, as discussed in moredetail below.

The trial implant is used to provide an indication of the location of astem trial relative to adjacent anatomical landmarks such as the lessertrochanter 6, the trochanteric fossa and the greater trochanter 8.

The trial implant comprises a stem trial 10 that can be received in theprepared intramedullary cavity in proximal femur. The stem trial mayhave cutting teeth 12 on its outer surface so that it can be used as abroach to prepare the cavity to receive the stem trial, and subsequentlythe femoral component of a hip joint prosthesis. The cutting teeth onthe stem trial mean that it can be used in steps that cut the bonesurface to shape the cavity and to compact the bone tissue that definesthe cavity.

The distal portion 14 of the stem trial 10 that is received in thediaphyseal region of the femur defines a stem axis 16 that is alignedwith the femoral axis when the stem trial is received in theintramedullary femoral cavity. The stem trial has a neck surface 18 thatextends at angle of about 45° to the stem axis.

The stem trial 10 is formed from stainless steel. The formation of stemtrials which have broaching teeth formed on their outer surface fromsuch materials is well known.

The trial implant includes a guide portion 20 that fits on to the stemtrial 10. FIGS. 2 through 4 show the guide portion in greater detail.The guide portion has a mating surface 22 that fits against the necksurface 18 on the stem trial. The mating surface on the guide portionhas a first socket 24 formed in it that can receive with a sliding fit afirst spigot on the neck surface of the stem trial. The mating surfaceof the guide portion has a second spigot 26 formed on it that can bereceived with a sliding fit in a corresponding second socket on the necksurface of the stem trial. The axes of each of the first socket 24 andthe first spigot 26 are perpendicular to the neck surface of the stemtrial. The first socket and the first spigot are spaced apart on theneck surface of the stem trial. The first spigot and the first socketare longer than the second spigot and the second socket to facilitatealignment of each of the spigot and socket pairs. The first spigot canbe tapered towards its tip to facilitate insertion into the firstsocket. The stem trial and the guide portion are located positivelyrelative to one another against translation and rotation when each ofthe spigots is received in its corresponding socket and the matingsurface 22 on the guide portion abuts the neck surface 18 on the stemtrial.

The guide portion 20 has a neck portion 28 that extends in a directionapproximately perpendicular to the mating surface 22. The neck portionhas first and second horizontal grooves 30, 32 formed in it, on each ofits principal opposite faces 34, 36. Each of the first and secondhorizontal grooves lies in a plane, the plane of the first horizontalgroove being parallel to the plane of the second horizontal groove, andspaced apart from it by about 4.8 mm. The plane of each of the first andsecond horizontal grooves is arranged at an angle of 45° to the matingsurface 22. This means that, when the guide portion 20 is mounted on thestem trial 10, with the mating surface 22 on the guide portion abuttingthe neck surface 18 on the stem trial, the plane of each of the firstand second horizontal grooves is approximately perpendicular to the stemaxis 16.

The neck portion 28 has a vertical groove 38 formed in it, on each ofits principal opposite faces 34, 36. The vertical groove intersects eachof the first and second horizontal grooves 30, 32 and is perpendicularto each of them. This means that, when the guide portion 20 is mountedon the stem trial 10, with the mating surface 22 on the guide portionabutting the neck surface 18 on the stem trial, the plane of thevertical groove is approximately parallel to the stem axis 16.

Each of the horizontal and vertical grooves 30, 32, 38 has a thicknessof 0.7 mm. Each of the grooves has a depth cut into the guide portion of3.5 mm. Each of the grooves is open at each of its ends where the grooveintersects the end faces 40, 41, 42, 43 of the guide portion.

The guide portion 20 can be formed from a metal such as a stainlesssteel or from a polymeric material such as a polyolefin, apolycarbonate, a PEEK, a polyamide, or a polyester. It can be formed bytechniques that include, for example, one or more of molding andmachining.

The assembly of the invention includes a plane guide 44 which is formedfrom a sheet of stainless steel. The plane guide is of a sufficient sizethat it extends from the guide portion 20 at least as far as the greatertrochanter 8, as shown in FIG. 1. The thickness of the plane guide isslightly less than the thickness of each of the horizontal and verticalgrooves 30, 32, 38 so that the plane guide is a snug fit in the grooves.In particular, the snug fit of the plane guide in a selected groove issuch that the portion of the plane guide that extends beyond the grooveis substantially fixed relative to the portion of the plane guide thatis located in the groove against movement out of the plane defined bythe groove.

FIG. 5 shows a proximal femur 2 with a trial implant that comprises astem trial 10 located within the intramedullary cavity with a trial neck50 and a trial head 52 fitted to it. The trial neck has a mating surfacewith a spigot and a socket formed on it, which cooperate with the spigotand the socket on the neck surface 18 of the stem trial so that the stemtrial and the trial neck are located positively relative to one anotheragainst translation and rotation when each of the spigots is received inits corresponding socket and the mating surface on the neck portionabuts the neck surface 18 on the stem trial.

The femur is prepared for receiving the trial instrument of theinvention using techniques that are commonly used in hip replacementsurgical procedures. These can include:

1. Pre-operative planning using X-ray or other images of the patient'sbone structure to identify provisionally the size and type of theimplant components that are to be implanted, and the required locationof each implant component relative to anatomical landmarks.

2. Resecting the femoral neck at a level identified during thepre-operative planning step with reference to the X-ray images. Theangle of the resection plane relative to the femoral axis will beselected according to the configuration of the intended femoralcomponent. For many implant components, the angle between the resectionplane and the femoral axis will be 45°. It can be preferred to resectthe neck at a level which is slightly above the final intended level sothat the bone can be finished on the final plane using a reamer.

3. Shaping the femoral canal using appropriate cutting tools such asosteotomes, rongeurs, reamers and broaches.

4. Compacting the cancellous bone in the femoral canal using one or moreimpactors and one or more broaches.

5. With the largest of the broaches left in place within the bonecavity, finishing the resected bone in the femoral neck using a calcarreamer, using the broach as a guide for the height and orientation ofthe reamer. This step defines the bearing plane for a collared stemcomponent which is ultimately to be implanted.

6. The guide portion of the trial implant is fitted to the stem trial.The guide portion is used to assess the position of the stem trialrelative to adjacent anatomical landmarks such as the lesser trochanter,the trochanteric fossa and the greater trochanter using a plane guide,fitted into the grooves on the guide portion of the trial implant. Ifthe position of the stem trial relative to the anatomical landmark isnot correct, it might then be appropriate to work further on shaping thebone cavity (using conventional cavity shaping techniques) until thetrial implant can be positioned correctly.

7. The guide portion is removed from the trial implant and is replacedby the trial neck with the trial head, which can then be used to assessrange of motion of the of the joint using an appropriate correspondingacetabular trial.

Subsequent steps in the procedure involve removal of the trialcomponents and implantation of implant components using techniques whichare conventional in hip joint replacement procedures.

What is claimed is:
 1. A trial instrument assembly for use in a surgical procedure to replace an orthopaedic joint, the assembly comprising: a. a trial implant having a stem portion for fitting within a prepared cavity in the patient's bone, the stem portion defining a stem axis, and a neck portion that is connected to the stem portion to protrude from the cavity when the stem portion is disposed within the cavity; and b. a plane guide that extends from the neck portion in a plane that is selected from (i) a plane perpendicular to the stem axis, and (ii) a plane parallel to the stem axis.
 2. The assembly of claim 1, wherein the plane guide is fixed to the trial implant.
 3. The assembly of claim 1, wherein the plane guide is removably fastenable to the trial implant.
 4. The assembly of claim 3, wherein one of the plane guide and the trial implant provides a first part of a projection and recess assembly and the other of the plane guide and the trial implant provides a second part of the projection and recess assembly, the projection being received in the recess to connect the plane guide with the trial implant.
 5. The assembly of claim 4, wherein the projection and recess assembly comprises a tongue and a groove, in which the tongue can be received in the groove to connect the plane guide with the trial implant.
 6. The assembly of claim 1, wherein the stem and neck portions of the trial implant are provided as separate components that comprise formations by which the components can be connected to one another.
 7. The assembly of claim 1, wherein the stem portion of the trial implant has an external surface and at least one cutting tooth formed on the external surface.
 8. A trial instrument assembly for use in a surgical procedure to replace an orthopaedic joint, the assembly comprising: a. a trial implant having a body portion for fitting within a prepared cavity in the patient's bone and a guide portion that is connected to the body portion to protrude from the cavity when the body portion is disposed within the cavity, the guide portion providing at least one first part of a projection and recess assembly; and b. a plane guide having a first portion that provides the second part of the projection and recess assembly and engages the first part of the projection and recess assembly, and a second portion that, when the second part of the projection and recess assembly is engaged with the first part of the projection and recess assembly, extends beyond the end of the second part of the assembly where the plane guide engages the first part of the assembly.
 9. The assembly of claim 8, wherein the body and guide portions of the trial implant are provided as separate components that have formations by which the said components can be connected to one another.
 10. The assembly of claim 9, wherein the formations comprise at least one spigot provided on one of the components and a corresponding socket on the other of the components in which the spigot can be received.
 11. The assembly of claim 8, further comprising a trial neck component that can be fitted to the body portion of the trial implant in place of the guide portion of the trial implant.
 12. The assembly of claim 8, wherein the body portion of the trial implant is a stem trial for use in preparing the femur in a hip joint replacement procedure or for use in preparing the humerus in a shoulder joint replacement procedure.
 13. The assembly of claim 8, wherein the guide portion of the trial implant provides two spaced apart first parts of a projection and recess assembly by which the trial implant can be connected to the plane guide, the two first parts defining first and second planes in which the first plane is parallel to the second plane.
 14. The assembly of claim 8, wherein the guide portion of the trial implant provides two first parts of a projection and recess assembly by which the trial implant can be connected to the plane guide, the two first parts defining define first and second planes in which the first plane is perpendicular to the second plane.
 15. The assembly of claim 8, wherein the parts of the projection and recess assembly that are provided on the trial implant are grooves and wherein the first portion of the plane guide defines a tongue that fits in a selected one of the grooves.
 16. A method of preparing a bone to receive an implant component in a surgical procedure to replace an orthopaedic joint, the method using an assembly as claimed in claim 8, and comprising: a. positioning the body portion of the trial implant in a prepared cavity in the patient's bone; b. engaging the parts of the projection and recess assembly provided by the first portion of the plane guide and the guide portion of the trial implant, so that the second portion of the plane guide extends beyond the trial implant; c. assessing the position of the second portion of the plane guide relative to an adjacent anatomical feature.
 17. The method of claim 16, wherein the body and guide portions of the trial implant are provided as separate components which have formations by which the components can be connected to one another.
 18. The method of claim 16, further comprising the steps of removing the guide portion of the trial implant from the body portion thereof, and fitting a trial neck component to the body portion of the trial implant in place of the guide portion thereof. 